Prior Art
Today, in the field of ceramics, a variety of products are being produced by the technology which comprises, in sequence, blending a starting ceramic powder with an organic binder to impart plasticity to the powder, injection-compacting the powder to obtain a green compact, removing the binder and sintering the compact. This process is characterized in that geometrically complicated parts which cannot be produced by press forming, for instance, can be manufactured commercially with good high-production reproducibility.
Meanwhile, in the field of sintered metal parts, it is by now a time-honored practice to manufacture sintered metal parts by the technology called powder metallurgy, that is the production technology which comprises adding a certain amount of an organic substance to a starting powder, shaping the powder by press forming, and sintering the compact. In recent years, however, for the commercial manufacture of geometrically complicated parts with good high-production reproducibility, attempts have been made to apply the above-mentioned injection compacting technology in use for ceramic products to the production of sintered metal parts.
However, the manufacture of sintered metal parts by the injection compacting technology has problems, for the following and other reasons.
(1) Whereas the average particle diameter of the starting powder used for ceramic products is as fine as 3 .mu.m or less, metal powders are comparatively coarse. PA0 (2) The starting powder for sintered metal parts has a high specific gravity in many instances as compared with the ceramic powder in general, such as alumina powder. PA0 (3) Compared with general-purpose ceramic powders, e.g. oxide type ceramic powders such as alumina powder, powdered metals are low in wettability with binders.
For those reasons, the deformation on removal of the binder is larger than it is the case with ceramics and if an attempt is made to produce sintered metal parts under conditions comparable to those in use for the production of ceramic parts, poor injection compactability, deficiencies in strength of the green compact, deformation of the green compact on removal of the binder and other troubles are encountered so that it is difficult to manufacture sintered parts comparable to ceramic parts in quality. Moreover, as experienced frequently, it is even impossible to obtain green compacts which worth sintering and, for this reason, the use of a special jig has been found necessary in some cases.